View Full Version : 12VDC solenoids?

05-23-2007, 05:50 PM
I've been learning from the archives, but haven't seen my particular situation addressed.

Question: anyone make 12vdc solenoids for sprinkler valves anymore?

Backstory: I want to control a drip line irrigation setup (2 or 3 zones) to water a veggie garden and there is no AC power available. I've a solar powered fence charger that uses a 12v battery that would be fine. I also have an older Rainbird ISA-408 controller which uses a 12vdc wall wart and obviously uses 12vdc to control the valves (solenoids).

I'm having trouble locating 12vdc solenoids since 24vac seems to be the norm, so experimentation indicates the ISA-408 will trip a modern valve, but it latches for some reason and stays open when it should've closed. If I disconnect the wire, the output from the controller goes to zero, like it's supposed to.

I've seen battery powered timers that attach to a hose bib, but they control one zone only and are usually low flow, like 5 gpm.

It'd be nice to use a modern 24vac timer but that's a long (200') extension cord or a control wire. Burying cable probably isn't feasible either since the field is likely to be tilled once or twice a year for a few years.

Kyle Accardi

05-23-2007, 07:07 PM
I don't know the answer to your question. But I lived somewhere that did extensive drip irrigation using a gravity-fed system. Not sure how they controlled zone valves or if they even had them.

05-23-2007, 08:17 PM
Hello Eric, thanks for the reply. I'm not sure I'm doing the smartest thing. I've little experience with drip irrigation, a smaller vegetable garden last year being the only real case.

I'm running off a well which is approx. 500' away from the site in question. I'm not yet sure what the actual well produces (until I can find the well-digger's report) but the flow-rate from the pump is around 7 gpm at 29 psi.

There are four beds each 40' long fed by 1/2" line. Think of a hair comb--each bed has 39 3' long drip lines spaced 12" apart (the tines of the comb).

I could give myself a headache and do the math, but intuition tells me that to push that much water will require the well pump to run for several hours at a time, and that dividing the beds into two zones will give me more control, and give the pump a break.

The smarter thing might be to fill a cistern above the beds (they are on a hill) and let gravity be my friend.


05-23-2007, 08:20 PM
I also have an older Rainbird ISA-408 controller which uses a 12vdc wall wart and obviously uses 12vdc to control the valves (solenoids).Obviously? Look again at that wall-wart. Rainbird does not supply DC wallwarts to run 24 vac valves. Doesn't mean you can't power a controller with one, since it can run from a backup battery. What it won't do, is switch DC power to valves.

What is your budget to deal with this situation?

05-23-2007, 11:46 PM
Sorry, I might have been vague. The controller I have is powered by a DC wallwart (labeled 9vdc but puts out 12vdc even under load). The online manual suggests that this model was made as late as 2001. It only mentions that "the ISA Series Timers can be used with most hydroindexing valves." Whatever that is.

I do know that they are not generating AC from DC, and that the controller uses 12vdc as valve control. The valves I am testing with did not come with the unit, I bought them today in a 24vac world. The ISA series of timers are still made, but they seem to be ac only.

Somewhere there are a bunch of antique (six years old) 12vdc valves which would make me happy.

As far as budget goes, $20US per valve. Might even pay that for only the solenoid if it screwed into the valves I already have.


05-24-2007, 04:13 AM
Show us a photograph of a Rainbird 9vdc wallwart. You cannot switch DC power with a controller that uses triacs to switch AC power. Won't happen. Get a genuine 24vac wallwart, and use standard valves. Ask Rainbird.com if you aren't sure.

As an aside, there was a usage of 12vdc solenoids for irrigation valves, and they still exist, for there may still be some solar-powered controllers that charged lead-acid batteries, and ran dc solenoids. But this was a (expensive) choice only when there wasn't a chance at getting AC power to a controller. Your budget doesn't have any room for dc operation of valves.

05-24-2007, 07:04 AM
I have been familiar with the ISA series controllers for at least 8 years, and in that time frame they have always been 24VAC. The only DC valves I have ever seen are the self-contained battery operated timer/valve combos from DIG. Useful where no source of power is available. Pricey.

At some point, you have to stop wasting gas driving around looking for something which may or may not exist, or which may cost more than a whole new valve when you find it!

05-24-2007, 11:12 AM
It occured to me last night that perhaps the wall wart that I have isn't the correct one and that someone before me had the same bright idea. They even went to the trouble to find a appropiate connector for the end.

So I pop the thing apart, see no obvious reason not to try giving it 24VAC. I'm an electronic repair tech, but didn't spend too much time tracing out the circuit. Worse that happens is I let the smoke out.

Surprise, no smoke & AC to the zone terminals. A triac will pass DC but it latches. Think I'll go to RadioShack and get an inverter (12VDC->120VAC) for $30 and plug in the 24vac wall wart.

Seems I'm always trying to do something the hard way...


05-24-2007, 03:19 PM
That Radio shack inverter will probably drain your battery overnight.

Try: http://www.powerstream.com/dc24.htm

These are 12-24 VDC converters, however if you're an electronic tech, you can open it up and take out the output diode(s) that convert the switching power back to DC.

The PST-DC2171 looks like it would work, don't know how easy it is to take apart.


Bob NH
05-25-2007, 07:21 AM
Be careful putting inverter power on some electronics. I blew a power tool battery charger by using it on an inverter. The new one had a tag on the cord that said "Using this on an inverter will damage the charger."

You might try putting 12 VDC on a 24 VAC valve and see if it will work. A coil has lower impedance at DC and may pull enough current to actuate the device.

05-25-2007, 01:51 PM
The Rainbird ISA-408 is a 24 volt unit:


Page 10 is the giveaway where it says:

NOTE: Make sure that the total draw of
the master valve or pump start relay plus
the draw of the valve does not exceed
0.650 Amps at 24 VAC, 60 Hz.

"You might try putting 12 VDC on a 24 VAC valve and see if it will work."

Bob the only problem with this is that the controller uses Triacs to switch the valves on, and you need AC to make the Triacs work right, I guess they turn on but don't turn off because there is no zero crossing of the DC power as there is with AC power.


05-25-2007, 06:42 PM
Rancher said, "...you can open it up and take out the output diode(s) that convert the switching power back to DC."

I assume you meant AC. That could work--with a little help from a dremel. Looks like their unit only draws 15mA with no load. That's better than the 400mA the plug in inverter I just picked up from RadioShack today.

Don't think it'll be a problem. The car battery I have in mind has lots of amp-hours to give. I can drag it down the hill and recharge it in the shop when necessary. Wife says not to get attached to her fence charger's solar panel...

What would be neat is to modify the controller so that its Master Valve output used the 9v from its own battery. Then you could trigger a latching relay to turn on the inverter when it was time to water.

Sorry, this is probably way too geeky. Thanks everyone for your ideas & help. I'll whip this together this weekend & see what happens.


05-26-2007, 10:31 AM
Rancher said, "...you can open it up and take out the output diode(s) that convert the switching power back to DC."

I assume you meant AC. No I said what I ment, the diode converts the switching "AC" power back to DC. Therefore if you take the diode out, you have AC.


05-26-2007, 05:29 PM
I'm lost, you said, "...you can open it up and take out the output diode(s) that convert the switching power back to DC."

Anyway, it'd probably be at some wacko frequency that would blow the RainBird's mind.


05-26-2007, 06:23 PM
Sorry, I'm stupid, mis-parsed your sentence.

Have a virtual (or real) beverage of your choice on me.